Had my Sennheiser BTNC 4.5s for about a year now. The battery would only need charging once or maybe twice a week but I seem to be getting the low battery warning a lot quicker now. It seems to sound an alarm off at 30% and then continues every few minutes. Previously these type of warnings were when the battery was about to die, not 30%. I understand the battery will lose some of its capacity over time but this seems quite significant and am not sure if it's the warning system been too aggressive or the battery performance has fallen off a cliff. Anyone experience similar issues? And how easy is it to replace a battery as I really like these headphones.